Literally the first thing you notice when holding an iPad 2 is how thin it is.
Physically, the iPad 2 does feel a bit lighter than the old iPad, but it’s the thinness that’s striking. Compared to the new iPad 2, my original iPad doesn’t feel heavy, but it does feel fat. Almost swollen. The rounded edges on the iPad 2 make it significantly more comfortable to hold in one hand. — John Gruber
If you’re into this kind of stuff (build quality, functional design) the iPad 2 feels like a huge improvement over the first iPad. Not to mention the speed increase and double the RAM.